The invention generally relates to the field of optical communications, and more specifically to optoelectronic devices.
Lasers have become integral components in science and engineering. Lasers convert a sufficient external source of energy into coherent light inside a resonant cavity through, inter alia, the use of optical feedback.
A relatively simple laser 100 may be built using a Fabry-Perot configuration as illustrated in FIG. 1. FIG. 1 illustrates a perspective view of a simplified compound semiconductor heterostructure. An active region 104 is sandwiched between cladding layers 106. The cladding layers 106 are further characterized in that they are oppositely doped. The cleaved facets 110 of the laser 100 provide optical feedback by acting as partially reflecting mirrors. The facets 110 also provide exits for the light. The cladding layers 106 are typically coupled to an external electrical source such as a voltage or current source. Some definite advantages of the Fabry-Perot configuration include that it is easy and relatively cheap to fabricate. However, one large drawback in the Fabry-Perot configuration is that it accentuates a number of modes as determined by the geometry of the laser 100. Thus, the spectral output from the Fabry-Perot configuration reveals that a substantial number of wavelengths may be significantly amplified when a sufficient voltage or current source is applied.
The development of the distributed feedback (DFB) laser created devices that predominantly lase in one mode. FIG. 2 illustrates a side view of a simplified DFB semiconductor laser 200. Similar to the previous structure 100, the DFB laser 200 has an active region 204 sandwiched between cladding layers 208 and 210 which are typically oppositely doped. However, one of the differences from the previous structure 100 is that the DFB laser 200 has an etched grating 212 which extends the length of the cladding layer 208. The periodic perturbations in refractive indices due to the grating 212 provide distributed optical feedback by means of Bragg scattering. By choosing the periodicity appropriately, typically by applying the Bragg condition, the device 200 provides distributed feedback at selected wavelengths. As such, a single-frequency laser may be achieved. However, the fabrication of DFB lasers has proven to be more costly and intricately more complex than the fabrication of lasers utilizing a Fabry-Perot configuration.
What is needed is a method and system for a single-frequency laser that is cost effective and easy to fabricate.
The present invention provides for a single-frequency laser for use in an optical communication system. The single-frequency laser includes a first cladding layer, a second cladding layer, an active layer and an approximately V-shaped thin-film interferometer filter. The active layer including a longitudinal axis is disposed between the first cladding layer and the second cladding layer. The thin-film interferometer filter extends through the active layer.
The present invention also provides for a single-frequency laser for use in an optical communication system. The single-frequency laser includes a first cladding layer, a second cladding layer, an active layer, an approximately V-shaped Fabry-Perot filter for transmitting and reflecting light and a regrowth region. The active layer includes a longitudinal axis and is disposed between the first cladding layer and the second cladding layer. The approximately V-shaped Fabry-Perot filter extends through the first cladding layer, the active layer and, at least partially, the second cladding layer, and is positioned approximately centrally in the laser. The regrowth region is positioned, at least in part, above the approximately V-shaped Fabry-Perot filter and adapted to guide transmitted light from the approximately V-shaped Fabry-Perot filter along an optical path substantially parallel to the longitudinal axis of the active layer.
The present invention provides for a laser having a first cladding layer, a second cladding layer, an active layer and a thin-film interferometer filter. The active layer including a longitudinal axis is disposed between the first cladding layer and the second cladding layer. The thin-film interferometer filter extends through the active layer.
The present invention further provides for a laser having a Fabry-Perot configuration which supports a plurality of optical modes. The laser includes a first cladding layer, a second cladding layer, an active layer and means for suppressing all, but one of the optical modes, of the plurality of optical modes. The active layer including a longitudinal axis is disposed between the first cladding layer and the second cladding layer. The suppressing means extend through the active layer.
The present invention provides for an optical communication system utilizing wavelength division multiplexing. The system includes an information input signal which is divided into a plurality of information signals, a plurality of single-frequency lasers, an optical waveguide, and a plurality of demultiplexers. Each information signal of the plurality of information signals is coupled to one single-frequency laser of the plurality of single-frequency lasers. Each single-frequency laser has a first cladding layer, a second cladding layer, an active layer disposed between the first cladding layer and the second cladding layer, and a thin-film interferometer filter extending through the active layer. The plurality of single-frequency lasers are coupled to the optical waveguide. The plurality of demultiplexers are coupled to the optical waveguide and are adapted to reconstruct the information input signal.
The present invention also provides for an optical communication system utilizing wavelength division multiplexing. The system includes a plurality of data transmission terminals, a plurality of single-frequency lasers, an optical waveguide, a plurality of demultiplexers and a plurality of reception terminals. Each data transmission terminal of the plurality of data transmission terminals is coupled to one single-frequency laser of the plurality of single-frequency lasers. Each single-frequency laser has a first cladding layer, a second cladding layer, an active layer disposed between the first cladding layer and the second cladding layer, and a thin-film interferometer filter extending through the active layer. The plurality of single-frequency lasers are coupled to the optical waveguide. The plurality of demultiplexers are coupled to the optical waveguide. Each demultiplexer of the plurality of demultiplexers is coupled to one reception terminal of the plurality of reception terminals.
The present invention provides for a process for making a single-frequency laser, the process including the steps of depositing a first cladding layer on a substrate, doping the first cladding layer, depositing an active layer on top of the first cladding layer, depositing a second cladding layer on the active layer, doping the second cladding layer oppositely from the doping of the first cladding layer, etching an approximately V-shaped groove through the active layer, and depositing a thin-film interferometer filter on top of the V-shaped groove.
The present invention provides for a method of suppressing all but one of the optical modes of a resonant cavity of a Fabry-Perot laser. The method extends a Fabry-Perot filter through the resonant cavity at an angle to a longitudinal axis of the resonant cavity, transmitting through the Fabry-Perot filter only one desired optical mode, and suppressing all optical modes besides the one desired optical mode.